The present invention relates generally to electronic oscillators, and in particular to electronic oscillator circuits formed in gate array cells.
An oscillator circuit is required on many semiconductor chips to generate a sine and/or square wave (off-chip). This square wave is then used as a clock signal for both on-chip and off-chip circuits
Prior art oscillator circuits suffer from significant signal-to-noise degradation due to noise injection at the points where externally connected elements are applied to the chip. In a typical configuration, the lines from an external crystal are connected across the input and inverting output of an amplifier to obtain the required feedback for oscillation. The non-inverting output then presents a square wave. However, such a connection causes external noise injected at the input line of the amplifier to be amplified. This noise amplification seriously degrades the signal-to-noise ratio at the non-inverting output of the circuit.
The invention as claimed is intended to remedy the above-described noise amplification problem while maintaining an approximate 50% duty cycle.